CO2矿化煤基固废制备保水开采负碳充填材料试验研究
Experimental study on preparation of negative carbon filling material forwater protection mining by CO2 mineralization of coal⁃based solid waste
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摘要: 煤炭资源开发利用过程中会产生大量的CO2以及粉煤灰等煤基固废,在“双碳”目标下,如能采用CO2矿化煤基固废制备充填材料,并将其充填在采空区里控制岩层移动,将会“变废为宝”,推动保水开采等绿色低碳技术发展。针对矿井充填现场难以满足CO2矿化所需高温高压高钙(“三高”)条件的问题,探索在常温常压条件下,采用常规低钙粉煤灰(“三常”)研制CO2矿化煤基固废负碳充填材料(Negative Carbon Filling Material,NCFM)。在NCFM反应过程中,原材料首先发生水化反应生成C-S-H凝胶、Ca(OH)2和CaCO3,再与CO2反应后生成SiO2硅胶。在此过程中,碱性激发剂加速C-S-H凝胶和硅胶的生成,使NCFM具有快速早强特征。随着NCFM进一步水化反应,碱性激发剂会促进火山灰反应的发生,进而促使更多水化产物的生成,有利NCFM长期强度的提高。在采用坍落度测试、凝结时间测试、单轴抗压强度(UCS)测试、X射线荧光光谱(XRF)、X射线衍射(XRD)和扫描电子显微镜(SEM)-X射线能谱仪(EDS)分析,以及热重分析(TGA)测试的基础上,研究了NCFM的力学性能和微观组织,阐明了NCFM的早期与长期强化机制。80%粉煤灰掺量的NCFM试样的UCS最大,3 d达2.70 MPa,28 d达5.12 MPa。NCFM的最大CO2吸收量为1.39 mg-CO2/g-NCFM。NCFM的研制提供了保水开采负碳充填材料,可推进形成CO2资源化利用、固废规模化处置、采空区再利用,以及保水开采等煤炭资源绿色化开采的协同技术途径,促进实现“碳炭置换”,助力加快能源资源领域“双碳”战略目标实现。Abstract: In the process of development and utilization of coal resources, large amounts of CO2, coal⁃fired fly ash, and other solid waste will be produced. In the “carbon peak, carbon neutral” prospect, if the coal⁃based solid waste backfill material can be mineralized using CO2 and filled the goaf to control the strata movement, it will enable to “turn waste into treasure”, thus promoting the development of green low⁃carbon coal industry. Aiming at the prob⁃ lem that it is difficult to meet the high temperature, high pressure and high calcium (“three high”) conditions required for CO2 mineralization at the mine filling site, a CO2 mineralized coal⁃based solid waste negative carbon fill⁃ ing material (NCFM) has been developed using conventional low⁃calcium fly ash (“three constant”) under ambi⁃ ent temperature and pressure conditions. In the process of the NCFM reaction, the raw materials first undergo a hydra⁃ tion reaction to generate the C—S—H gel, Ca(OH)2 and CaCO3, and then react with CO2 to generate the SiO2 sili⁃ ca gel. In this process, the basic activator accelerates the formation of C—S—H and silica gel, which makes the NCFM to have the characteristics of high early strength. As the NCFM further hydrates, the alkaline activator pro⁃ motes the pozzolanic reaction, leading to the formation of more hydration products, which enhance the long⁃term strength of the NCFM. Incorporating mechanical properties and microstructure of the NCFM via slump test, setting time test, uniaxial compressive strength ( UCS ) test, X⁃ray fluorescence ( XRF ) spectrum, X⁃ray diffraction ( XRD ), scanning electron microscope ( SEM ), X⁃ray spectrometer ( EDS ) analysis, and thermogravimetric analysis (TGA) test, the early and long⁃term strength development mechanism of the NCFM is elu⁃ cidated. The UCS of the NCFM samples with 80% fly ash content is the highest, reaching 2.70 MPa in 3 days and 5.12 MPa in 28 days. The maximum CO2 absorption of 1 g NCFM was 1.39 mg. The development of the NCFM nega⁃ tive carbon backfill material is feasible to utilize in the green mining, simultaneously promote the coal resource green mining in a collaborative way, such as the CO2 recycling and large⁃scale solid waste disposal, goaf reuse, and water protection. Thus, it enhances “carbon⁃coal substitution”, and speeds up the energy resources “double carbon” strategic target realization.